Sea water destructible booster assembly



Dec. 1Q, 1968 T. 2. BALI.

SEA WATER DESTRUCTIBLE BOOSTER ASSEMBLY Filed March 31, 1967 FIG u f v o n n INVENTOR- Thomas 2. Ball FIG.3

United States Patent 3,415,188 SEA WATER DESTRUCTIBLE BOOSTER ASSEMBLY Thomas Z. Ball, New Ringgold, Pa., assignor to Atlas Chemical Industries, Inc., Wilmington, Del., a corporation of Delaware Filed Mar. 31, 1967, Ser. No. 627,481 8 Claims. (Cl. 10224) ABSTRACT OF THE DISCLOSURE In the art of explosive boosters, a sea water destructible member positioned in barrier relation with an explosive booster assembly to render same sea water destructible in the event of misfire and which is thus particularly useful for offshore seismographic exploration.

The present invention relates to a sea water destructible booster assembly. More particularly, the present invention relates to a member containing a high percentage of magnesium and positioned in barrier relation with an explosive booster assembly for use in salt water seismographic exploration.

Explosives used in marine seismographic exploration may include an electric explosion initiator, a booster and a main explosive charge which is fired underwater. Occasionally, such explosives may accidentally fail to fire or may break away from a firing line. Boosters presently employed in seismographic explosives may remain potentially useable under great depths of sea water for long periods of time without desensitization of either the contained electric initiator or the booster explosive. A dangerous situation may thus exist as the result of a potentially detonable initiator and booster assembly being washed up or dragged from the sea.

It has now been found that by providing a member containing a high percentage of magnesium which is positioned in barrier relation with an explosive booster assembly, there results a sea water destructible booster which is desensitized in the event such as of misfire of the explosive in offshore seismograph exploration.

In accordance with the present invention, a booster assembly is rendered seawater destructible by including a member containing a high percentage of magnesium suitably positioned to permit desensitization of the booster assembly by the ingress of sea water after the member containing the high percentage of magnesium is dissolved. The magnesium member is desirably positioned in barrier relation between sea water and the contained explosive charge of the booster assembly.

The booster assembly of the present invention may be prepared as illustrated in the accompanying drawing in which like numerals represent the same elements throughout the several views.

In the figures: 1

FIG. 1 is a half-section view taken as a partial side elevation and illustrating a booster assembly prepared by the present invention;

FIG. 2 is a top elevational view of the booster assembly of FIG. 1; and

FIG. 3 is a half-section view taken as a partial side elevation and illustrating an alternate bottom casing for use with the member containing a high percentage of magnesium of the present invention.

FIG. 1 illustrates booster assembly having shell 12 in which may be positioned detonating charge 14. The detonating charge may be fired by an electric explosion initiator, not shown, or related initiator which is positioned in cap well 16.

A member containing a high percentage of magnesium illustrated as barrier washer 18 is provided and held in position by the crimped walls of shell 12. Barrier washer 18 is suitably secured to cap Well 16 by the flanged outer wall of the cap well as illustrated. When introduced into sea or salt water, barrier washer 18 is thus disposed intermediate the sea or salt water and the contained explosive charge of the booster assembly.

The member containing a high percentage of magnesium may be formed of substantially pure magnesium, or as an alloy of magnesium of about to about 97% by weight of magnesium with other metals. A particular useful alloy is one having about 2 to about 3 A% by weight of aluminum, about 0.5 to about 1.5% by weight of zinc, up to about 0.05% by weight of copper, about 0.2% or slightly more by weight of maganese, with the remainder being substantially composed of magnesium.

The thickness of the member containing a high percentage of magnesium may vary and depends upon the length of life desired for the booster assembly. It is found that a suitable thickness for the magnesium member is one sufiicient to support a cap well while crimped in position near the top of the booster shell while thin enough to be dissolved by about a 3% aqueous sodium chloride solution within about seven days. A useful thickness range for the magnesium member is between about 0.015 inch to about 0.075 inch. A thickness range of about 0.025 inch to about 0.035 inch for the magnesium member is preferred since it is found that such a thickness will be dissolved by about a 3% aqueous sodium chloride solution within about 25 to about 72 hours thus permitting a contained explosive to be effectively detonated within the customary period for seismic explosives, i.e., within about 5 hours, while being totally desensitized thereafter in the event of misfire. The interval between the period of effective detonation and total desensitization provides a useful safe period for detonation.

It is recognized that although the member containing a high percentage of magnesium may be a barrier washer for convenience of manufacture, various other sections of the present booster assembly may also contain such a member of magnesium. For example, cap well 16 or booster shell 12 may be constructed of a high percentage of magnesium. Alternately, a combination of areas in barrier contact between the sea or salt waterand the contained explosive of the booster assembly may be constructed of material containing a high percentage of magnesium.

Shell 12 is desirably formed of various materials such as plastic; waterproof paper; metal such as iron, copper, high percentage magnesium, or aluminum and may include aperture 20 to provide an ingress means for water which aids to render the assembly water destructible.

A water-dispersible sealing plug, not shown, formed of polyvinyl alcohol or other water-dispersible material such as methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, polyvinylpyrrolidone, polyvinyl methyl ether, sodium and potassium salts of polyacrylic acid, and the present high percentage magnesium material, or the like may be included to seal aperture 20. Thus on immersion of the assembly in salt or sea water, the water-dispersible sealing plug resists the ingress of water into shell 12 for a prec-alculated period of time sufficient to permit the detonator to be fired. Thereafter, the assembly will be destroyed by salt or sea water which dissolves the member containing a high percentage of magnesium at one end of shell 12 and by water which enters shell 12 by aperture 20 and ultimately destroys the booster assembly 10 by providing a means for detonating charge 14 to be washed out of shell 12.

Although aperture 20 is illustrated near the bottom of shell 12, it is recognized that the aperture may be positioned at any convenient location about the shell such as near the member containing a high percentage of magnesium, i.e., barrier Washer 18, to increase the rate at which the assembly may be destructed by sea water. Magnesium member 18 may be thus dissolved by sea water attaching both the external and internal surfaces thereof.

FIG. 2 illustrates a top view of booster assembly of FIG. 1.

In the embodiment of FIG. 3, water ingress aperture of FIG. 1 is removed to prevent water from entering shell 22 except by way of the magnesium member illustrated as barrier washer 18 disposed near the top of booster shell 12 as illustrated in FIG. 1.

Detonating charge 14 is positioned adjacent to cap well 16 and in detonating relation thereto. The detonating charge may include any suitable material such as cyclotrimethylenetrinitriamine, pentaerythritol tetranitrate, nitrostarch, trinitrotoluene, tetryl or the like.

It is understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A sea water destructible explosive booster assembly which comprises, a shell having an explosive contained therein, and a member containing a high percentage of magnesium and selected from the group consisting of substantially pure magnesium and an alloy of magnesium containing about 90% to about 97% by weight of magnesium, said member positioned in barrier relation to said shell for containing said explosive and having a thickness which is dissolvable by about 3% aqueous sodium chloride solution within about 7 days.

2. The booster of claim 1 wherein the shell is provided with a water ingress means.

3. The booster of claim 1 wherein the member containing a high percentage of magnesium is of a thickness which is dissolvable by about 3% aqueous sodium chloride solution within about 25 to about 72 hours.

4. The booster of claim 1 wherein the member containing a high percentage of magnesium is a barrier Washer which supports a cap well in the center thereof.

5. The booster of claim 4 wherein the said washer has a thickness of about 0.015 inch to about 0.075 inch.

6. The booster of claim 4 wherein the said washer has a thickness of about 0.025 inch to about 0.035 inch.

7. The booster of claim 2 wherein the water ingress means is provided with a water-dispersible sealing plug.

8. The booster of claim 7 wherein the water-dispersible sealing plug is a member of the group consisting of polyvinyl alcohol, methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, polyvinylpyrrolidone, polyvinyl methyl ether, sodium and potassium salts of polyacrylic acid, and a high percentage magnesium material.

References Cited UNITED STATES PATENTS 3,279,372 10/1966 Patterson 102-28 3,322,066 5/1967 Griffith et al 10224 3,356,024 12/1967 Driscoll et al. 10228 3,358,600 12/1967 Grifi'ith et a1. 102-24 3,358,601 12/1967 Dittmann et al 102--28 OTHER REFERENCES Materials, vol. 60, No. 5, N.Y., Reinhold, October 1958, pp. 158 to 162.

BENJAMIN A. BORCHELT, Primary Examiner.

VERLIN R. PENDEGRASS, Assistant Examiner. 

